This application claims the priority of German Patent Application Serial No. 199 42 609.0, filed Aug. 31, 1999.
The present invention relates, in general, to press fitting elements, and in particular to a metallic press fitting element.
A press fitting system of carbon steel or high-alloy steel as well as copper for home installation is known, for example from published brochures by mapress mannesmann pressfitting-system, Lieferprogramm Sanitxc3xa4r, Heizung, September 1998, or mapress Kupfer March 1999. This system includes essentially a deformable press fitting element which is available in many designs, e.g. as elbow, T-piece, coupling or adapter, and has a radially outwardly projecting bead area for interiorly accommodating a sealing ring. Formed inwardly of and connected to the bead area via a slanted transition is a cylindrical portion which extends in longitudinal direction. At the end, the cylindrical portion is formed with a radially inwardly projecting crease-like depression for providing a stop surface for a pipe being inserted into the pipe fitting element and having a smooth end. The bead area terminates in a straight end portion, as viewed in longitudinal cross section, and extends perpendicular to the longitudinal axis of the press fitting element. The wall thickness of the straight end portion equals the wall thickness of the bead as well as of the cylindrical portion, and the terminal radial end of the straight end portion bounds a circular opening. The inner diameter of the non-deformed sealing ring, which forms a torus, is at least equal to or greater than the inner diameter of the cylindrical portion.
By applying two clamping jaws of a pressing tool, the bead area is subject to a plastic deformation whereas the trapped sealing ring is subject to an elastic deformation. In addition, during this pressing process, a crease-like depression is formed in the cylindrical portion of the press fitting element in immediate proximity of the bead and penetrates also the pipe located underneath. The elastically deformed sealing ring assumes in this joint system the sealing function, while the formed crease-like depression absorbs longitudinal forces applied by the internal pressure as well as a fraction of the torque. During plastic deformation of the bead, a more or less pronounced burr formation is unavoidable in the closing zone of the clamping jaws. Size and type of the burr depends on the contour of the press fitting element, on the flow behavior of the material being squeezed, and on the tolerances between the pair of press fitting elementxe2x80x94clamping jaw. A comparison of materials used in the sanitary and heating fields, that is carbon steel, high-alloy steel and copper, clearly shows that the flow behavior of copper greatly deviates from the flow behavior of steel. Thus, to use the proven contour of a press fitting element of steel for press fitting elements of copper is unfavorable as far as burr formation is concerned. As a matter of fact, also the burr formation in press fitting elements of steel is not satisfactory at all to date.
Since introduction of the pressing process of a fitting with inserted pipe more than 25 years ago, pressing tools with clamping jaws that match a nominal size being respectively pressed are increasingly available on the market. Currently, there are more than 150,000 clamping jaws on the market. The advantage of pipe joints by a pressing process instead of welding, soldering, screwing, or sticking has been recognized in the meantime even by such conservative users involved in the heating and sanitary fields so that a need is created to expand the field of application of the pressing process also for use with materials other than carbon steel or high-alloy steel. The manufacturer of such pressing systems has to take into account thereby the possibly different flow behavior of materials newly included in the system. For example, this is evident for copper compared to carbon steel or high-alloy steel. One proposal involved the adaptation of the contour of the clamping jaw to the different flow behavior. This, however, requires the user to stock two sets of tools for each nominal size, rendering this proposal cost-intensive and entailing a risk of confusion as well as requiring greater spatial demands. These shortcomings evidently convinced the users to reject this proposal and the need to double the number of clamping jaws to be stocked.
It is thus an object of the present invention to provide an improved press fitting element, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved press fitting element of metal, in particular copper, which can be pressed together with an inserted pipe, regardless of the flow behavior of the material being used while utilizing the commercially available clamping jaws of a pressing tool with proven cross section for differently standardized dimensions and yet attaining an unobjectionable quality without undesired burr formation.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing, at a same nominal wall thickness of the cylindrical portion and the bead area including the radially extending straight end portion, the transition between the cylindrical portion and the bead area with an inside slant which extends in relation to a horizontal at an angle of 34xc2x0 to 37xc2x0, thereby reducing an axial length of the bead area compared to conventional press fitting elements.
The configuration of a press fitting element in accordance with the present invention has the effect that at a same depth of penetration of the clamping jaw, the volume being squeezed is smaller so that burr formation is eliminated or at least appreciably diminished. Still, the sealing ring is sufficiently compressed elastically to maintain the sealing action at operating conditions. This is also helped by dimensioning the circular opening, which is bounded by the radially extending straight end portion, with a diameter that is greater than the inner diameter of the cylindrical portion by 0.8 mmxc2x10.2 mm. This prevents a premature contact of the straight end portion upon the pipe during pressing process and an interference with the pressing action of the bead area.
Tests have shown that the proposed contour of the press fitting element leads to a reduced burr formation, regardless of the material being used. However, the change in contour is still not sufficient for press fitting elements of copper. Therefore, according to another feature of the present invention, the cord diameter of the sealing ring, associated to a nominal size, is reduced and the bead area is decreased to a same extent. The nominal wall thickness is retained, as is the diameter of the circular opening of the radially extending straight end portion. The decrease of the cord diameter of the sealing ring is at least 0.2 mm, preferably 0.5 mm, in order to implement the desired effect. A decrease of the cord diameter by more than 1 mm may result in leakage.